Method of manufacturing racket frames



1960 TOKICHI OKA METHOD OF MANUFACTURING RACKE'I' FRAMES Filed April 5,1956 \llilllll mea'anaa...m...

INVENTUR TIJKIEHI UKA BY M ATTURNEY METHOD or MANUFACTURING RACKET IFRAMES Tokichi Oka, Yokohama City, Japan Application April 5, 1956,Serial No. 576,306

1 Claim. (Cl. 154-90 The present invention relates to sport rackets,such as are used for tennis, badminton, squash, etc., and par-.

ticularly toa method of manufacturing the bow and shank frame thereof.

Sidewise motion refers to motion of the bow with respect to the handlein the plane defined by the stringing. Rotary motionrefers to motion ofthe bow with respect to the handle about the longitudinal axis of thehandle. Backward andforward motion refers to motion in a plane includingthe longitudinal axis of the handle, said plane being perpendicular tothe plane of the stringing. It is absolutely necessary for sport racketsto have the combined resiliency of. sidewise, rotary, andforwardbackward motion. Heretofore, there has never been any'satisfactory. method of manufacturinga racket frame for providing thedesired requirement to meet the abovementioned toughness andresiliencies.

Heretofore the oval frame of a sport racket has been made of bent wood.The manufacturing process has been so complicated that it includes manysteps, such as, bending high quality wood, gluing it together, andsurface finishing by abrasion. Although the manufacturing cost has beenvery expensive, the racket frames so manufactured have not satisfied thedesired requirements in hard play. Cracks and destruction are veryfrequent. Wear is severe.

Furthermore, the most important problem of manufacturing a high qualityracket frame with the desired toughness is-to select a suitable woodmaterial for use in the frame thereof. Heretofore, the wood materialbest fitted for use in a racket frame is one of the rarest naturalresources found in the high mountains. Accordingly, the cost of the bestwood material is very high. I have solved the hardest problem inchoosing material in the process of my invention. In accordance with myinvention, any kind or quality of wood can be used. High quality wood ofthe rarest kind is not necessary.

I can choose whatever wood is available in the market as a framematerial for a sport racket. I can convert the most inferior quality ofwood into the highest quality material for the frame of a sport racket.

It is one object of the invention to provide a method of manufacturing aracket frame of superior quality in an inexpensive manner.

It is another object of the invention to provide a method ofmanufacturing a racket frame in which mass production thereof ispossible.

Another object of the invention is to provide a very simple method ofmanufacturing a racket frame of great strength almost equal to that ofmetal.

Another object of the invention is to reduce the manufacturing cost ofracket frames and improve the quality thereof.

With the above and other objects in view that will hereinafter appear.the nature of the invention will be more fully understood by followingthe detailed description, the appended claims, and the views illustratedin the accompanying drawings, in which:

United States Patent Fig. 1 is a side view of a bow frame and shankthereto,

.showing a string of glass fiber superposed on both sides thereof andanother string of glass fiber coiled on and bow frame and shank coiledwith glass fiber is inserted,

with the mold partly broken away.

Fig. 3 is a section of the bow frame and shank manufactured inaccordance with my invention, showing wood core 5, coiled glass fiber 8,and superposed thermosetting resin 9.

In the preferred method of manufacturing a racket frame in accordancewith my invention, the wood material for use'in an oval frame of a sportracket is a very insignificant matter. As described hereinbefore, I canchoose whatever wood is available in the market as a racket frame. Theselection of material is a very important problem in any manufacturingindustry, particularly in manufacturing high quality racket frames.

Heretofore the bow frame of a sport racket has been formed by bending aperipheral member such as a laminated ash strip into a closedcurvilinear shape such as an oval. I can dispense with such a difficultstep of bending wood. I punch a fiat sheet of cheap wood into an ovalshape by the punch press. I punch not only an oval frame, but also ashank thereto. Next I put-a string of glass fiber on both sides of theframe and shank, and wind another string of glass fiber around theframe'and shank into. a coil, the core of which is the wooden frame andshank. Then I pour a liquid polyester resin into the lower half of themetallic mold into which a bow frame and shank can be inserted, insertthe bow frame and shank coiled completely with the glass fiber into themold, pour the liquid polyester resin again on it, cover it with theupper half of the mold, and heat the mold to cure the resin therein.Lastly I take the cured molded bow frame and shank out of the mold and Ipolish it, according to the method of my invention.

Referring more particularly to Fig. 1, I punch a bow frame 4 and shank 6thereto out of a flat sheet of wood, superpose a string of glass fiber 7on both sides of the bow frame and shank, and coil another string ofglass fiber 8 on and around not only the bow frame 4, but also the shank6 closely and tightly. The amount of glass fiber depends on the desiredstrength and weight of an athlete. l have found, however, that aboutSOparts of glass fiber based on the weight of wood as 100 parts isfavorable and suitable for a light weight racket for use in badminton.The glass fiber is preferably treated with chromium sulphate.

Referring to Fig. 2, I put the bow frame and shank coiled with glassfiber in the lower half part 2 of a metallic mold, the recess of whichcorresponds to the shape of the bow frame and shank. The recess of themold has a clearance into which a suitable amount of thermosettingresin, such as polyester resin, is filled. I prefer to pour somethermosetting resin prior to inserting the bow frame and shank.Furthermore, the metallic mold is preferably first coated with chromiumor silicone resin in order to impart good separability. Besides, Iprefer to preheat the mold to the temperature of C. Having put the bowframe and shank coiled with glass fiber into the mold, I pour the restof the resin on it. The amount of resin also depends upon the desiredstrength and weight of a racket. I have found, however, that about 50parts of resin based on the weight of wood as parts is suitable andsuificient for a light weight racket for use in badminton. Then I coverit with the upper half part 1 of the mold and press it slowly with thepressure of about ten pounds per square centimeter. The pressure doesnot matter in my invention. A pressure to squeeze excess resin out ofthe clearance of the mold is suflicient for my purpose. 1 heat the moldincluding the bow frame and shank therein to a temperature between 140C. and 150 C. for a time sufficient to cure the resin, preferablybetween one and two minutes. After the completion of polymerizationin'the mold, I take the molded product out of the mold.

In the event the polymerization is delayed, it can be mentioned bowframe and shank punched out of the flat sheet of wood by the method ofmy invention.

The manner of coiling a string of glass fiber on and around the bowframe and shank may be variously changed and modified, such as, coilingglass fiber closely and tightly, coiling it roughly in spaced intervals,coiling it in an oblique manner, etc., except that one must leaveuncovered the spaced apertures 10 in which catgut string is received.

From the foregoing description, taken in connection with theaccompanying drawings, it is considered that the novel details ofconstruction, and the advantages of the invention, will be apparent tothose skilled in the art to which it relates.

It is of course, to be understood that the details of structure may bevariously changed and modified without departing from the spirit andscope of my invention as set forth in the appended claim.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent, are:

In a method of manufacturing a bow frame for sports rackets comprisingthe steps of punching a frame and shank from a stock of wood material,applying strings of glass fiber on both sides of said frame and shank,winding another string of glass fibers into a coil around the woodenframe and shank, pouring a liquid polyester resin into the lower half ofa mold, inserting said bow frame and shank coiled with said glass fibersinto the lower half of said mold, pouring a second application of'liquid polyester resin on ,said "frame and shank, covering the lowerhalf of said mold with the upper half thereof, heating said mold to curesaid resin, removing said cured molded bow frame and shank from saidmold, and polishing'said bow frame and shank. 9

References Cited in the file of this patent UNITED STATES PATENTS2,285,031 Hickman June 2, 1942 2,541,297 Sampson et a1. Feb. 13, 19512,573,361 Rodgers et a1. 2 Oct. 30, 1951 2,594,693 Smith Apr. 29, 19522,602,766 Francis July 8, 1952 2,626,804 Robinson Jan. 27, 19532,695,178 Rheinfrank Nov. 23, 1954 2,749,643 Scott June 12, 1956 FOREIGNPATENTS 162,109 Australia Mar. ,22, 1955

